The long-term goal of this project is to better understand the tissue microenvironment that controls the activity and behavior of epithelial stem cells. Epithelial stem cells are responsible for the maintenance and regeneration of self-renewing tissues such as epidermis, hair follicle, and mammary gland. We have begun analyzing the biology and function of subdermal adipocytes during skin tissue homeostasis. In mammals, depots of white adipose tissue store energy through lipid accumulation and can serve as paracrine signaling tissues. In the skin, subdermal adipocytes compose a unique adipose tissue depot that underlies the dermal fibroblasts and surrounds the hair follicle during hair growth. Data suggests that adipocytes may regulate hair follicle cycling and wounding, but the role of subdermal adipocytes in the skin is not known. Our preliminary data shows that subdermal adipocytes are essential for hair follicle cycling and wound healing and generate a dynamic microenvironment in the skin. We hypothesize that the interplay between skin cells and subdermal adipocytes is crucial for the regulation of epidermal homeostasis. To address this hypothesis, we will: 1. characterize whether subdermal adipocytes are important for maintaining the hair follicle stem cell phenotype by a. analyzing mice with genetic or pharmacologically induced defects in adipogenesis, resulting in defects in subdermal adipocytes and b. defining adipogenesis during the hair cycle. 2. determine if subdermal adipocytes play a role in epidermal wound healing by a. defining the wound healing response in mice with defects in subdermal adipocytes and b. defining the cellular mechanisms that lead to adipocyte regeneration during wound healing. 3. Define the molecular mechanisms by which subdermal adipocytes regulate skin homeostasis using in vitro assays with adipocytes to address the role of signaling molecule expression by these adipocytes in the skin. Patients with alopecia, hair shaft disorders, or chronic wounds could potentially benefit from this research. PUBLIC HEALTH RELEVANCE: A thorough understanding of the regulation of epithelial stem cell behavior by the surrounding tissue environment is a crucial requirement for tissue-specific regenerative therapies to effectively treat human disease. The manner in which different cell types in mammalian tissues interact is largely unknown. We will define how a major but poorly understood cell type in the skin, subdermal adipocytes, act to control epidermal homeostasis and repair, establishing an essential mammalian model to study an intact tissue environment. Our work will improve our ability to create skin tissue for future therapies and will also have global relevance for other regenerative tissues, where adipocytes operate to maintain tissue homeostasis.